The study of developmental defects caused by environmental contaminants has been focused mostly on mammal. In mammalian teratology, it has become clear that functional impairment is a more subtle response to toxicants than the production of gross anatomical abnormalities. A considerable amount of attention is now being devoted to "behavioral teratology," i.e. behavioral abnormalities in anatomically normal animals after embryonic exposures. There has been little attention paid to this aspect of developmental responses of fish embryos to environmental pollutants. A recent study (Weis and Weis in press) showed that larvae of the mummichog which were exposed as embryos to 5 or 10 ppb methylmercury (concentrations below those which cause structural malformations) were less effective in capturing prey than were controls. These larvae were morphologically normal, and therefore this response can be considered an example of behavioral teratology in fishes. Impaired prey capture by adult mummichogs in a Hg-contaminated area has been observed, raising a number of questions. This proposal is to investigate the development of this impaired behavior, i.e. at what point in larval or juvenile development it sis first manifested. If it is present at the time of hatching due to embryonic exposure to toxicants, it would be an example of behavioral teratology. This proposal is also to investigate other toxicants to see if they cause behavioral teratology in fish embryos, which could be a model system for this developing field of research.